1. Field of the Invention
The present invention relates to a motorized wheelchair having right and left motorized type rear wheels, and nonturning-type omni-directional front wheels having a plurality of rollers rotatable in a direction orthogonal to an alignment direction of the wheels are disposed for direction change around the wheels.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Application Publication No. 8-56991 or Japanese Unexamined Patent Application Publication No. 10-179651, a two-wheel-drive motorized wheelchair is known, in which the wheels are rotatable with a circumferential surface of each wheel in a pressure contact state by drive rollers by attachably/detachably mounting a motor-driven drive unit for the auxiliary drive on the rear wheels of the motorized wheelchair. Further, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-344289, a four-wheel-drive motorized wheelchair is known, in which a pair of drive units are provided on either side of the wheelchair to independently drive front and rear wheels on one side and front and rear wheels on the other side, a plurality of rollers rotatable in a direction orthogonal to an alignment direction of the wheels are disposed around a rim of each of the pair of front wheels, each roller being formed in a half-spindle shape in which the diameter of a tip portion is smaller than the diameter of a base end portion so that an outer circumference of the wheel is defined by the circumferential surface of each of the rollers, the tip portion of each of the rollers being partially inserted into a recess formed in the base end portion of an adjacent one of the rollers so as to be brought close to the adjacent base end portion, and the treads of the front wheels and the rear wheels being identical to each other.
The four-wheel-drive motorized wheelchair disclosed in the above-described Japanese Unexamined Patent Application Publication No. 2004-344289 can stably travel on a slope and an uneven road, smoothly pass over irregularities and steps, and can realize high road ability in an alignment direction. Further, high steering stability can be obtained due to the interlocking type design in the front-rear direction of the wheelchair. Still further, the steering is performed in a differential rotational manner due to the speed difference between the wheels on either side, the turning radius during turning can be reduced comparison with that of wheelchairs with an existing steering design, and a floor surface is not damaged when the wheelchair is steered indoors. Still further, an omni-directional wheel having rollers of a half-spindle shape to be partially inserted into the counterparts is employed for the right and left front wheels. Since the treads of the front and rear wheels are identical each other, noise is reduced, the wheelchair can be driven smoothly in an alignment direction or a turning direction, and catching of stones in a space between the rollers can also be suppressed.
However, when the four-wheel drive is always performed, and if a traveling area of the four-wheel drive wheelchair is not flat and any one of the wheels is idle, power is wasted, and a problem occurs, in that the circumferential surface of rollers of the omni-directional wheels can be easily damaged by the frictional rotation. On the other hand, in the case of a two-rear-wheel-drive motorized wheelchair, the center of gravity is moved forward when traveling downhill, the ground contact force of the rear wheels is reduced, the brake performance and the steerability are degraded, and the road ability is degraded when the wheelchair travels on an uneven road surface. Further, another problem occurs, in that wheels can become easily stuck in a single direction travels in a case of a wheelchair with the caster type front wheels on a road surface inclined in the transverse direction.